Color issue with workflow between FCP7 and CS3

At the production studio I work at we are having an issue with our outputs. We shoot primarily against green screen, cut the video in FCP7, output it to AE CS3 for keying, and then kick it back to FCP7 for finishing work.

The issue is that when kicking it to AE the picture becomes darker and seems a little yellowish. We were originally passing off Pro Res files but the gfx team recommended switching to AIC because it was easier for AE to handle the file size and they didn't have the ProRes codec on their system. They've downloaded QT7 just recently but haven't tried pro res footage in the program yet to see if its easier to work with now.

Could the issue be with the codec? My thought is ProRes is better to use but is AIC suffice?

Is the issue with using CS3? Would the issue be resolved if we used CS5.5? (not able to upgrade to CS6 yet)

[Matt Ferguson]"Could the issue be with the codec? My thought is ProRes is better to use but is AIC suffice?"

Yup, I'm afraid that the codec's the culprit. AIC may be smaller, but there's a reason for that: loss of image quality, and that isn't good.

[Matt Ferguson]"...the gfx team recommended switching to AIC because it was easier for AE to handle the file size and they didn't have the ProRes codec on their system"

I'm not sure what they mean that it's easier for AE to handle smaller files. That's a head-scratcher, because my copy of AE CS3 has no problems with large files. Nor does my Windows box running AE at home. Using ProRes HQ, even. Non-FCP-equipped machines with an up-to-date version of QT 7 can read ProRes 422, but they can't write to the codec. They can, however write to HQ.

There may be another reason why they're talking about the files being too big. Maybe they're running out of storage. It happens.